Method And Fixture For Twisting End Portions of Bar Conductors, In Particular For Bar Windings of Electric Machines

ABSTRACT

A twisting method ( 100 ) is described, for twisting free end portions ( 2 A,  3 A,  2 A′,  3 A′) of bar conductors ( 1, 1′ ) for the stator or rotor bar winding of an electrical machine, comprising: 
     a step of providing ( 101 ) a twisting fixture ( 10 ) comprising at least a pocket member ( 11 ) extending about a twisting axis (Z-Z) and provided with a circular array (S 1 ) of pockets having its center on the twisting axis (Z-Z), the pocket member ( 11 ) including a main structure ( 11 A) provided with an arc (R 1 ) of adjacent pockets of said array (S 1 ) and a secondary structure ( 11 B) which is movably mounted with respect to main structure ( 11 A) and which is provided with a further pocket ( 11 B′) of said array (S 1 ), each of the pockets of said array (S 1 ) comprising a respective insertion opening ( 11 A″,  11 B″), which is adapted to be passed through by one of said free end portions ( 2 A,  2 A′) for inserting such free end portion into said pocket; 
     a step of providing ( 102 ) a stator core ( 20 ) or rotor core ( 20 ) provided with a plurality of slots ( 24 ) which are populated by a respective plurality of said bar conductors ( 1, 1′ ) which are arranged with said free end portions ( 2 A,  2 A′) protruding from a side of stator core ( 20 ) or rotor core ( 20 ), said protruding end portions forming a circular array (T 1 ) of end portions ( 2 A,  2 A′); 
     a step of inserting ( 103 ) into the arc (R 1 ) of pockets of the main structure ( 11 A) an arc of adjacent end portions ( 2 A,  2 A′) of said array of end portions (T 1 ); 
     a first step of twisting ( 104 ) the arc of end portions, which is inserted into said arc (R 1 ) of pockets, by relative rotational-translational motion between said core ( 20 ) and said pocket member ( 11 ); 
     the method being characterized in that it further comprises: 
     a step of axially translating ( 105 ) the secondary structure ( 11 B) with respect to the main structure ( 11 A), for inserting, into said further pocket ( 11 B′) of the secondary structure ( 11 B), a further end portion ( 2 A) of said array (T 1 ) of end portions; and 
     a second step of simultaneous twisting ( 106 ), by means of a further relative rotational-translational motion between said core ( 20 ) and said pocket member ( 11 ), the arc of end portions, which is inserted into the arc of pockets (R 1 ) of the main structure ( 11 A), and further end portion ( 2 A,  2 A′), which is inserted into the further pocket ( 11 B′) of the secondary structure ( 11 B).

The present invention refers to a twisting method and fixture fortwisting free end portions of bar conductors, in particular for statoror rotor windings of electric machines.

It is known to provide stators or rotors of electric machines, likeelectrical generators or motors, for example for use in hybridelectrical vehicles (HEVs), wherein the stator or rotor winding iscomposed of a plurality of bar conductors, which are bent and variouslyinterconnected to each other in order to provide so called bar windings.

In particular, the known art comprises bar windings composed of barconductors having a rectangular cross section, where the term“rectangular” refers to a square section as well as to a “flat” section,generally indicating a rectangular section, wherein two sides of thesection are smaller than the other two.

So called bar conductors are usually preformed by “U” or “P” bending,starting from linear bar conductors. United States patent U.S. Pat. No.7,480,947 describes an exemplary method for pre-forming bar conductors(called “hairpin conductors” in this document). “U” or “P” preformedconductors, often also called “basic preformed conductors” in thetechnical field, typically have two adjacent legs, of different length,each provided with a free end portion and an opposed end portion, whichis joined, by means of a joining portion, to the other leg.

For example, in order to provide a stator, it is known to carry out twodifferent types of twisting on the “U” or “P” preformed conductors.

In a first type of twisting, also called “twisting from the insertionside”, the basic preformed conductors are adequately inserted incorresponding radially aligned pockets, which are provided in a twistingdevice, suitable for deforming, after insertion, such conductors. Thetwisting device is essentially used for “driving apart” the legs of the“U” or “P” shape, in order that both legs of same conductor, afterextracting the latter from the twisting device, may be successivelyinserted into slots of a stator core, which are radially offset to eachother by a predetermined pitch.

Published patent application U.S. 2009/0178270 describes an exemplary“insertion side” twisting method, for uniform-pitch twisting ofpreformed bar conductors after their insertion into pockets of atwisting device.

After having undergone the first type of twisting, the bar conductorsare inserted into the slots of the stator core through a first side ofsame (the so called “insertion side”) with respective free end portionsprotruding from a second side of core (the so called “welding side” or“connection side”), which is opposed to the first side.

The free end portions protruding from the welding side are thensubjected to a second type of twisting, also called “welding sidetwisting”, after being inserted into pockets provided in a suitabletwisting fixture. The twisting fixture's goal is to bend (“twist”) thefree end portions of conductors in order to adequately shape such endportions and therefore allow the provision of adequate electricalconnections between conductors in order to complete the winding.

It is to be noted that precision bending of free end portions ofconductors facilitates the forming of connections among conductors.However, for various reasons, it may be difficult to correctly andprecisely bend the free end portions of conductors, as required.

For example, since the protrusion of the majority of these end portionson the welding side is relatively small, it may be difficult to accessthe end portions of conductors and carry out the operations required toensure a correct bending both in the circumferential and in the axialdirection with respect to the stator core axis. Moreover, as an example,a precise shaping of conductors is complicated by the fact that theseare provided with an intrinsic elasticity, which, after bending, triesto drive them partially back to their starting configuration.

Published U.S. patent application 2009/0302705 describes an exemplarywelding side twisting method of above said type. The method described inthis patent application allows at one time to achieve non uniformtwisting of free end portions of bar conductors. In order to providesuch twisting, the patent application describes a twisting fixturecomprised of a pocket member, which is provided with a lost motionmember, for defining a pocket of pocket member. In particular, the lostmotion member is mounted circumferentially movable with respect to amain structure of pocket member.

It is felt the necessity to provide an alternate twisting method, withrespect to the above said known art, for twisting free end portions ofbar conductors for bar windings of electric machines.

The present description's general objective is to provide a twistingmethod, which is able to satisfy above said necessity.

This and other objectives are reached by a twisting method as defined inclaim 1 in its more general form, and in its dependent claims, in somespecific embodiments of the same.

A further aim of the present invention is to provide a twisting fixtureas defined in claim 6 in its more general form, and in the dependentclaims, in some specific embodiments of the same.

The invention will be more clearly understood from the followingdetailed description of its embodiments, which are illustrative andtherefore not limiting with respect to appended drawings, wherein:

FIG. 1 shows a perspective view of a currently preferred embodiment of atwisting fixture for twisting free end portions of bar conductors, inparticular for windings of electric machines, wherein the twistingfixture is shown in a first operating configuration;

FIG. 2 shows a perspective view of fixture of FIG. 1, wherein thefixture is shown in a second operating configuration;

FIG. 3 shows a plan view from above of fixture of FIG. 1 in the firstoperating configuration;

FIG. 4 shows a view from above of fixture of FIG. 1, in the secondoperating configuration;

FIG. 5 shows four perspective views of four components of fixture ofFIG. 1;

FIG. 6 shows four perspective views of four other components of fixtureof FIG. 1;

FIGS. 7A-7C show three perspective views of a bar conductor, in threedifferent configurations, respectively;

FIGS. 8A-8C show three perspective views of a further bar conductor,suitable for being used as phase terminal, which is shown in threedifferent configurations, respectively;

FIG. 9 shows a perspective view, wherein the fixture of FIG. 1 in thefirst operating configuration and a stator or rotor core for anelectrical machine having a plurality of bar conductors inserted inrespective slots are shown, wherein the core and the fixture are shownin their entirety in a third operating configuration;

FIG. 10 shows a further view of core and fixture of FIG. 9, shown in aperspective section in third operating configuration, wherein somecomponents of twisting fixture have been removed;

FIG. 11 shows a perspective view of core and fixture of FIG. 9,generally shown in a fourth operating configuration;

FIG. 12 shows a further sectional and perspective view of core andfixture of FIG. 9 in a fourth operating configuration;

FIG. 13 shows an enlarged detail of FIG. 12;

FIG. 14 shows a further perspective view of core and fixture of FIG. 9,wherein the core and fixture shown are in the fourth operatingconfiguration;

FIG. 15 shows a front plane view of an embodiment of a twistingapparatus comprising the twisting fixture of FIG. 1; and

FIG. 16 shows a flow chart of a twisting method.

In the appended figures, same or similar elements are indicated by thesame numeral references.

In the present description, a “flat” or “square” bar conductor indicatesa bar conductor having four essentially flat sides, each joined toadjacent sides, typically by a rounded edge.

Therefore, the words “flat” or “square” or equivalent terms used todescribe the cross section of a bar conductor, are used in a generalsense, and should not be interpreted as excluding the fact that such barconductors have significantly rounded edges joining the substantiallyflat sides. The term “flat conductor” is to be regarded as meaning thatthe conductor has two opposed sided, whose mutual distance is greaterthan the distance between the remaining opposed sides. In the presentdescription, the term “rectangular conductor” is to be regarded as ageneralization of a flat and square conductor, since the squareconductor is a special case of a rectangular conductor, wherein the foursides have the same size.

In the present description, a pocket may be defined as a recess ordepression in a member, which is completely surrounded by this member,as well as by a cavity in a member, wherein an open side of cavity issuch as to be effectively closed by a surface or wall of an adjacentmember.

For the purposes of the present description, the term “twisting” usedwith reference to end portions of bar conductors, is to be regarded in ageneral sense as a bending or shaping of such portions, in order toprovide adequate electrical connections among conductors.

For the purposes of the present description, the terms “radial” or“circumferential” or other similar expressions defined with respect to adirection or axis, have to be referred to a circumference, which lies ona plane perpendicular to such direction or axis and is centered on suchdirection or axis. Moreover, for the purposes of the presentdescription, the term “angularly spaced” (or other similar expressions),defined with respect to a direction or axis, refers to the angle betweentwo radii of a circumference, which lies in a plane which isperpendicular to said direction or axis, and whose center lies in saiddirection or axis.

Initially referring to FIGS. 7A and 8A, two embodiments of barconductors 1, 1′ for a stator or rotor winding of an electrical machineare respectively shown. In this example, conductors 1, 1′ are flatrectangular copper conductors, since they have a pair of opposed faces,whose mutual distance is greater than the distance between the other twoopposing faces.

As is shown in FIG. 7A, the conductor 1 is a first pre-formed “P” shapedconductor, having two legs 2, 3 which are connected by a connectionportion 4, and each having a respective free end portion 2A, 3A. Theconnection portion 4 is also frequently called “head portion” in therelevant art sector. As may be noted in FIG. 7A, leg 2A is slightlylonger than leg 3A.

The conductor 1′ shown in FIG. 8A is a second bar conductor, inparticular a conductor suitable for being used as a phase terminal,having a shape which is essentially identical to that of conductor 1,except for the fact of having an leg which is significantly longer thanthe other. In particular, conductor 1′ comprises two legs 2′, 3′, whichare connected by a connection portion 4′ and each having a respectivefree end portion 2A′, 3A′.

Referring now to FIG. 1, 10 generally indicates a currently preferredembodiment of a twisting fixture for twisting free end portions of barconductors for bar windings of electric machines. For example, fixture10 is suitable for twisting free end portions 2A, 3A and/or free ends2A′, 3A′ of a plurality of bar conductors 1, 1′.

The twisting fixture 10 comprises at least one pocket member 11,extending about a twisting axis Z-Z. The preferably ring shaped pocketmember 11 comprises a main structure 11A and at least one secondarystructure 11B, which is movably supported with respect to main structure11A.

According to a currently preferred embodiment shown in FIG. 5, the mainstructure 11A has an annular shape, which in this example is essentiallycylindrical.

In FIG. 6, a plurality of secondary structures 11B is shown, inparticular five secondary structures 11B, according to a currentlypreferred embodiment. In particular, the secondary structures 11B inFIG. 6 may be coupled to the main structure 11A of FIG. 5, in order toprovide the pocket member 11. In the embodiment of FIG. 6, the secondarystructures 11B are fixed to each other by means of a curved support base11C, for rigidly connecting to each other the end portions of structures11B. According to further embodiments, however, the secondary structures11B may be separated from each other. In other words, the structures 11Bmay also be completely distinct structures, which may be independentlyactuated.

With reference to FIG. 3 or 4, it may be noted that the pocket member 11is provided with a circular array of pockets S1, whose center lies onthe twisting axis Z-Z. The array S1 comprises a plurality of pockets11A′, 11B′, which are respectively defined by the main structure 11A andsecondary structures 11B and are such as to globally form the array S1.The array S1 in the example comprises 72 pockets. It is to be noted thatin FIGS. 3 and 4, the twisting axis Z-Z is perpendicular to the drawingplane and is schematically represented by a cross.

Pockets 11A′, 11B′ are each provided with an insertion opening 11A″,11B″, or inlet opening 11A″, 11B″, through which a respective free endportion of bar conductor may pass, for example one of end portions 2A,3A, 2A′, 3A′ of conductors 1, 1′, in order to allow such portion to beinserted in the respective pocket. As may be noted, openings 11A″, 11B″in this example have a substantially rectangular shape and arepositioned on preferably planar end faces of the main structure 11A andsecondary structures 11B, respectively. Such end faces are in particulartransversal or essentially perpendicular to the twisting axis.

The main structure 11A is such as to define at least a pocket arc R1comprised of a plurality of adjacent pockets 11A′ of array S1. As isshown in FIG. 5, in this example, the main structure 11A is providedwith a plurality of pocket arcs R1. More in particular, the structure11A is comprised of three pocket arcs R1, which are angularly spacedwith respect to twisting arc Z-Z, each comprising a different number ofpockets 11A′. As is shown in FIG. 5, beside the three arcs R1, in thisexample, structure 11A is such as to define two further pockets 11A′,which are angularly spaced to each other and which in particular have anaxial extension (Z-Z axis) which is greater than that of the otherpockets 11A′.

Turning back to FIG. 3 or 4, it is to be noted that pockets 11A′ of eacharc R1 are angularly and uniformly distributed. In other words, as isshown in FIG. 3 or 4, centers of two adjacent pockets 11A′ are angularlyspaced from each other by a same predetermined angle A1 with respect totwisting axis Z-Z. In this example, angle A1 is in particular equal to5°.

Still referring to FIG. 3 or 4, it is to be noted that each secondarystructure 11B is such as to define at least one pocket 11B′ of array S1.In other words, each secondary structure 11B defines at least a furtherpocket 11B′ of array S1, in addition to pockets 11A′ defined by mainstructure 11A.

In the exemplary embodiment, the secondary structures 11B are such as todefine each a pocket arc R2 including a plurality of adjacent pockets11B′. In particular, also pockets of arcs R2 are angularly and uniformlydistributed, so that centers of two adjacent pockets 11B′ are angularlyspaced from each other by a same predetermined angle A2, with respect totwisting axis Z-Z. In this example, angle A2 is equal to angle A1, i.e.5°.

However, it is to be noted that pockets 11B′ of each secondary structure11B are all circumferentially offset in a direction by a predeterminedquantity with respect to pockets 11A′. In other words, as is for exampleshown in FIG. 3, centers of adjacent pocket 11A′ and pocket 11B′ areangularly spaced with respect to twisting axis by an angle which is notequal to said angles A1, A2.

The secondary structures 11B are axially slidably mounted, i.e. they mayslide in the direction of the twisting axis Z-Z, with respect to mainstructure 11A. More in particular, secondary structures 11B are adaptedto translate in the direction of the twisting axis Z-Z only, withrespect to main structure 11A. In other words, structures 11B arerotationally integral with main structure 11A about twisting axis Z-Z.Again in other words, each structure 11B is essentially provided onlywith one degree of freedom with respect to main structure 11A. In thisexample, in order to allow said axial sliding, secondary structures 11Bare coupled to main structure 11A by means of precision couplings. Withreference to FIG. 5, in order to provide such precision couplings, thepocket member 11 preferably includes a plurality of slide seats 12, inthis example five slide seats 12, each defined by a pair ofcircumferentially opposed pair of guiding walls 12′, 12″. Particularly,a respective secondary structure 11B is slidable in each seat 12.

With reference to FIGS. 1 and 2, it is to be noted that each secondarystructure 11B is such as to take up an axially backward operatingposition (FIG. 1) and an axially forward operating position (FIG. 2)with respect to the axially backward position.

As may be noticed in FIG. 1, in the axially backward position (Z-Zaxis), each secondary structure 11B is such as to define a recess 13 orcavity 13 of the pocket member 11. In particular, in such position,insertion openings 11B″ of structures 11B are positioned at a firstaxial distance (Z-Z axis) of insertion openings 11A″ of pocket arcs R1of main structure.

With reference to FIG. 2, in the axially forward position (Z-Z axis),the insertion openings 11B″ of pockets 11B are positioned at a secondaxial distance from inlet openings 11A″ of arcs R1 of main structure11A. Such second axial distance is preferably less than the first axialdistance. In the currently preferred exemplary embodiment, when thesecondary structures 11B take up the axially forward position, theinsertion openings 11B″ are, in particular, flush (FIG. 2) withinsertion openings 11A″. According to a further embodiment, in theaxially forward position of structures 11B, openings 11B″ may besubstantially flush with insertion openings 11A″, instead of beingperfectly flush with said openings. In this case, openings 11B″ arepreferably positioned in an axially backward position with respect toinsertion openings 11A″, wherein their distance from latter openings ispreferably equal to some millimeters, for example 1 mm-3 mm.

Referring now to FIGS. 1, 5 and 6, it is to be noted that, according toa currently preferred embodiment, the twisting fixture 10 comprises atleast a pair of pocket members. In particular, in this example, thefixture 10 comprises two pairs of pocket members 11, 14 and 15, 16,which are mutually coaxial. In this example, as may be noted from FIGS.5 and 6, members 14, 15 and 16 display some structural differences withrespect to member 11. However, such members have characteristicscorresponding to and a function essentially analogous to those of member11. In other words, members 14, 15, 16 respectively comprise, as anexample (FIGS. 1, 6 and 6):

a circular array of pockets S2, S3, S4;

a main structure 14A; 15A, 16A, provided with at least one pocket arc,including a plurality of pockets 14A′, 15A′, 16A′ provided withinsertion openings 14A″, 15A″, 16A″; and

at least one secondary structure 14B, 15B, 16B, which is axiallyslidably mounted (Z-Z axis) with respect to main structure 14A, 15A,16A, the secondary structure 14B, 15B, 16B being provided with at leastone pocket 14B′, 15B′, 16B′ with an insertion opening 14B″, 15B″, 16B″.

Referring now to FIG. 11, there is shown fixture 10 and stator or rotorcore 20. For example, core 20 is the core of a stator or rotor of anelectric machine, such as for example an electric motor, for example foran electric or hybrid vehicle.

As known per se, the core 20 comprises a lamellar tubular main body,axially extending along a stator axis (which corresponds, in FIGS. 9-12,to twisting axis Z-Z) between two opposing faces 22, 23, which arecalled insertion face 22 and welding face 23, respectively. Main body ofcore 22 comprises a plurality of slots 24, which axially extend (i.e. inthe direction of stator axis) inside the thickness of main body andwhich may be passed through by a plurality of bar conductors. In thisexample, in particular, core 20 comprises seventy two slots 24. More inparticular, slots 24 are angularly and uniformly distributed so thatcenters of two adjacent slots 24 are angularly spaced with respect totwisting axis, by an angle equal to above said angle A1, i.e. 5°.

According to an embodiment, slots 24 of core 20 are populated by twocrowns 25, 35 of bar conductors, in particular, a radially internalcrown 25 and a radially external crown 35. In this example, the crownexclusively comprises a plurality of conductors 1 (FIGS. 7A-7C) whereascrown 35 comprises of both a plurality of conductors 1 and a pluralityof phase terminals 1′ (FIGS. 8A-8C).

With reference to FIGS. 9 and 10, wherein core 20 is partially shown, itmay be noted that conductors and 1′ are inserted into slots 24 withrespective free end portions 2A, 3A and 2A′, 3A′, protruding fromwelding face 23. It is also to be noted that, in FIGS. 9-13, conductors1 and 1′ inserted into core 20 have respective shape of FIGS. 7B and 8B.In other words, such conductors have respective legs 2, 3 and 2′, 3′separated by a predetermined quantity, for example following a twistingoperation of “head portions” 4, 4′ (such twisting is known to theskilled in the field and is therefore not further described). It is alsoto be noted that free end portions 2A, 3A, 2A′, 3A′ of FIGS. 9-13 arestraight end portions, i.e. without any bending.

With reference to FIG. 12, wherein core 20 and fixture 10 arerepresented in a perspective section, it may be noted that legs of barconductors are positioned inside the core 20 so that they form fourcircular concentric arrays of legs, and therefore, four circularconcentric arrays of free end portions T1, T2, T3, T4, protruding fromwelding face 23. In particular, free end portions of each array T1-T4are preferably flush or essentially flush to each other, except for freeend portions 2A′ of phase terminals 1′ of array T1, which form asignificant protrusion with respect to other end portions 2A of arrayT1.

Moreover, as is shown in FIG. 12, the end portions of arrays T1-T4 areradially aligned to each other with respect to twisting axis Z-Z.

An exemplary operation of a twisting fixture, as previously described,is described in the following.

In FIG. 9, fixture 10 and core 20 are represented in an insertionconfiguration of bar conductors 1, 1′ in pocket members 11, 14, 15, 16.In FIG. 9, fixture 10 in particular take ups an initial configurationcorresponding to configuration of FIG. 1. In other words, all thesecondary structures 11B, 14B, 15B and 16B of pocket members 11, 14, 15,16 take up above said axially backward operating position (downwardbackward position in the figures).

Core 20 is initially supported at an axial distance (Z-Z axis) fromfixture 10, the end portions of arrays T1-T4 being directed towardspocket arrays S1-S4. It is to be noted that arrays T1-T4 are associatedto respective arrays S1-S4.

Core 20 and fixture 10 are then axially brought together (Z-Z axis) inorder to insert one part of end portions 2A, 3A, 2A′, 3A′ of arraysT1-T4 into pockets of main structures 11B, 14B, 15B and 16B of pocketmembers. In this way, the arrangement of FIGS. 11 and 12 is obtained.

It is to be noted that, in such an arrangement, all pockets 11A′, 14A′,15A′, 16A′ of main structures 11A, 14A, 15A, 16A internally receive arespective free end portion of arrays T1-T4. It is also to be notedthat, with this arrangement, since the secondary structures 11B, 14B,15B, 16B are in said backward position, the end portions of arrays T1-T4which are not inserted into pockets of main structures 11A, 14A, 15A,16A, are positioned outside of pockets 11B′, 14B′, 15B′, 16B′ at anaxial distance (Z-Z axis) from insertion openings 11B″, 14B″, 15B″, 16B″of secondary structures 11B, 14B, 15B, 16B.

It is also to be noted that in the arrangement of FIG. 11 or 12, thefree end portions of arrays T1-T4 which are not inserted into pockets ofmain structures 11A, 14A, 15A, 16A, are axially offset to each other(Z-Z axis) with respect to corresponding pockets of secondary structures11B, 14B, 15B, 16B, by a predetermined angle with respect to twistingaxis. This offset between the end portions of arrays T1-T4 and pocketsof secondary structures 11B, 14B, 15B, 16B is shown, as an example, inFIG. 13, where some end portions of array T4 are shown, which areaxially offset with respect to corresponding pockets 16B′ of one 16B ofsecondary structures.

In this example, each of end portions of arrays T1-T4 which are notinserted into pockets of main structures 11A, 14A, 15A, 16A, is axiallyoffset with respect to corresponding pocket (i.e. with respect to pocketof secondary structure 11B, 14B, 15B, 16B, in which said end portion isto be inserted), by an angle equal to half the angle A1 or A2 (which isalso equal to the angle between two adjacent slots 24), i.e., in thisexample, by an angle of 2.5°. In any case, it is appropriate to pointout that, in general terms, in order to avoid interferences among thefree end portions of conductors during twisting, it is important thatabove said offset corresponds to an angle less than angle A2 between twoadjacent pockets 11B′.

Starting with arrangement of FIG. 11, the pocket members 11, 14, 15 and16 are rotationally actuated about twisting axis Z-Z and aresimultaneously translated in the axial direction, in particular bybringing the fixture 10 closer to the core 20, in order to carry out afirst twisting only of end portions of arrays T1-T4 which have beeninserted into pockets of main structures 11A, 14A, 15A, 16A. Inparticular, pocket members are each rotated in an opposite directionwith respect to adjacent pocket member, in order to twist the endportions of arrays T1-T4 in opposite directions.

In other words, in order to carry out the first twisting, fixture 10 andcore 20 are subject to a relative rotational-translational motion,preferably in a continuous way, with respect to twisting axis Z-Z. Inthis regard, it is to be noted that, in principle, therotational-translational relative motion may be attained by differentways. For example, assuming the twisting of only one of arrays T1-T4, bymeans of a twisting fixture including only one pocket member, forexample, member 11, the arrangement may be such that the pocket memberis held still and the core 20 is rotated and translated. On the otherhand, one may rotate the pocket member, wherein the core 20 issimultaneously translated towards such member. However, alternatemethods, with respect to the one described for achieving said relativerotational-translational motion, are generally less advantageous.

In this example, at the end of first twisting, pocket members 11, 14, 15and 16 have each progressed through a rotation with respect to twistingaxis which is equal to 2.5°. Therefore, the free end portions of arraysT1-T4, which were initially axially offset with respect to correspondingpockets, at the end of first twisting, are axially aligned withcorresponding pockets of secondary structures 11B, 14B, 15B and 16B.

It is also to be noted that such end portions remain outside of pocketsof secondary structures 11B, 14B, 15B and 16B, during the whole firsttwisting.

Moreover, at the end of first twisting, such end portions are stillstraight end portions, whereas the end portions which are inserted intothe pockets of main structures 11A, 14A, 15A and 16A are bent endportions.

At the end of first twisting step, starting from the axially backwardposition, secondary structures 11B, 14B, 15B and 16B are axiallytranslated with respect to main structures 11A, 14A, 15A and 16A,simultaneously in this example, in order to insert the remaining endportions of arrays T1-T4 into pockets of secondary structures 11B, 14B,15B and 16B. In other words, secondary structures are actuated in orderto axially translate until they take up the above said axially forwardposition (FIG. 2), at which the remaining free end portions of arraysT1-T4 are received within pockets of secondary structures. Inparticular, in such an arrangement, the insertion openings 11B″, 14B″,15B″ and 16B″ of secondary structures are flush or substantially flushwith insertion openings 11A″, 14A″, 15A″ and 16A″ of pockets of mainstructures. Moreover, in such a configuration, free end portions whichare inserted in pockets of secondary structures 11B, 14B, 15B and 16Bare still straight, i.e. free of bends.

Once the protruding end portions of all arrays T1-T4 are inserted intopockets of fixture 10, a second twisting is carried out, wherein all endportions of arrays T1-T4 are simultaneously bent by further relativerotational-translational motion between core 20 and pocket members offixture 10. The second twisting is carried out in substantiallyanalogous way to first twisting. However, in the second twisting, thepocket members of this example carry out a greater rotation with respectto twisting axis Z-Z. In particular, in this example, at the end ofsecond twisting, each pocket member has carried out an additionalrotation by 20° with respect to that of first twisting. Therefore, inthis example, the end portions which had been subject to first twistingare subject, in total, to a twisting by 22.5° at the end of secondtwisting, whereas end portions which have only been subject to secondtwisting are subject to a total twisting by 20°. By means of fixture 10it is therefore possible to carry out a non uniform twisting of free endportions of arrays T1-T4.

FIG. 14 shows the core 20 and fixture 10 at the end of second twistingstep. It is to be noted that in this configuration, conductors 1, 1′ ofthis example are respectively arranged as shown in FIG. 7C and 8C.

With reference to FIG. 16, based on above said operation of fixture 10,it is to be noted that, generalizing such operation has been described atwisting method 100 for twisting free end portions of bar conductors forbar windings of electric machines, comprising:

a) a step of providing 101 a twisting fixture 10 comprising at least apocket member 11 extending about a twisting axis Z-Z and provided with acircular array S1 of pockets having its center on the twisting axis Z-Z,the pocket member 11 including a main structure 11A provided with an arcR1 of adjacent pockets of said array S1 and a secondary structure 11Bwhich is movably mounted with respect to main structure 11A and which isprovided with a further pocket 11B′ of said array S1, each of thepockets of said array S1 comprising a respective insertion opening 11A″,11B″, which is to be passed through by one of said free end portions 2Aor 2A′ for inserting said free end portion into said pocket;

b) a step of providing 102 a stator core 20 or rotor core 20 providedwith a plurality of slots 24 which are populated by a respectiveplurality of said bar conductors 1, 1′ positioned with said free endportions 2A, 2A′ protruding from a side of stator or rotor core 20, saidprotruding end portions forming a circular array T1 of end portions 2A,2A′;

c) a step of inserting 103 into arc R1 of pockets of main structure 11Aan arc of adjacent end portions 2A, 2A′ of said array of end portionsT1;

d) a first step of twisting 104 the arc of end portions, which isinserted into said arc R1 of pockets, by relativerotational-translational motion between said core 20 and said pocketmember 11;

e) the step of axially translating (Z-Z axis) 105 the secondarystructure 11B with respect to main structure 11A, for inserting, intosaid further pocket 11B′ of secondary structure 11B, a further endportion 2A or 2A′ of said array T1, in addition to the arc of endportions which are inserted into said arc R1; and

f) a second step of simultaneous twisting 106, by means of a furtherrelative rotational-translational motion between said core 20 and saidpocket member 11, the arc of end portions, which is inserted into thearc of pockets R1 of main structure 11A, and further end portion 2A,2A′, which is inserted into further pocket 11B′ of secondary structure11B.

According to an embodiment, the twisting method 100 comprises a step,before the first twisting step 104, of making the secondary structure11B to take up an axially backward operating position with respect tomain structure 11A, such as, while said arc of end portions is insertedin the arc R1 of pockets, the further end portion 2A or 2A′ may bepositioned outside the further pocket 11B′ at a certain axial distancefrom insertion opening 11B″ of said pocket 11B′.

According to an embodiment of the twisting method 100, during the firsttwisting step 104, said further end portion 2A or 2A′ remains outsidethe further pocket 11B′.

According to an embodiment of method 100, before the first twisting step104, while said arc of end portions is inserted into said arc R1 ofpockets, the further end portion 2A or 2A′ is axially offset withrespect to the further pocket 11B′ by a predetermined angle with respectto twisting axis Z-Z, whereas at the end of first twisting step 104, thefurther end portion 2A or 2A′ is axially aligned with further pocket11B′.

According to an embodiment of method 100, the step of axiallytranslating 105 comprises a step of positioning the insertion opening11B″ of further pocket 11B′ flush or substantially flush with insertionopenings 11A″ of pockets of said arc R1.

With reference to FIG. 15, it is to be noted that above said method maybe carried out, as an example, by means of a twisting apparatus 200,including fixture 10, in which the core 20 may be disposed. Inparticular, apparatus 200 comprises for example actuating elements 210,which may be coupled to fixture 10 for actuating pocket members and, inparticular, said secondary structures. As an example, actuating elements210 may comprise electrical axes or other servo-fixtures of thehydraulic or pneumatic type. Moreover, apparatus 200 comprises at leastone pressure element 220 for engaging and containing connection portions4, 4′ during twisting process.

Based on above description, it is therefore possible to understand howabove said twisting method and fixture allow to satisfy above saidnecessity.

Moreover it is to be noted that the provision of a secondary structure,which is axially slidably mounted with respect to main structure ofpocket member, wherein the secondary structure is provided with aplurality of pockets, advantageously facilitates a strengthening ofsecondary structure with regard to stresses, in particular in acircumferential direction, which may occur during twisting. Again, alsothe provision of coupling secondary structure to main structure by meansof a precision coupling, advantageously facilitates an increasesreliability and strength of twisting fixture. Generally speaking, it isto be noted that a twisting fixture according to the present descriptionallows a particularly efficient and reliable twisting, and is at thesame time characterized by a relatively simple and robust structure.

Based on the principle of the invention, the ways to carry out the sameand its particular embodiments may be subject to ample modificationswith respect to the description and illustrations, which are merelyillustrative and non limiting, without departing from the scope of theinvention, as defined in the appended claims.

1. Twisting method (100) for twisting free end portions (2A, 3A, 2A′,3A′) of bar conductors (1, 1′) for a stator or rotor bar winding of anelectrical machine, comprising: a step of providing (101) a twistingfixture (10) comprising at least one pocket member (11) extended about atwisting axis (Z-Z) and provided with a circular array (S1) of pocketshaving its center on the twisting axis (Z-Z), the pocket member (11)including a main structure (11A) provided with an arc (R1) of adjacentpockets of said array (S1) and a secondary structure (11B) which ismovably mounted with respect to main structure (11A) and which isprovided with a further pocket (11B) of said array (S1), each of thepockets of said array (S1) comprising a respective insertion opening(11A″, 11B″), which is adapted to be passed through by one of said freeend portions (2A, 2A′) for inserting such free end portion into saidpocket; a step of providing (102) a stator core (20) or rotor core (20)provided with a plurality of slots (24) populated by a respectiveplurality of said bar conductors (1, 1′) which are arranged with saidfree end portions (2A, 2A′) protruding from a side of the stator core(20) or rotor core (20), said protruding end portions forming a circulararray (T1) of end portions (2A, 2A′); a step of inserting (103) into thearc (R1) of pockets of the main structure (11A) an arc of adjacent endportions (2A, 2A′) of said array of end portions (T1); a first step oftwisting (104) the arc of end portions, which is inserted into said arc(R1) of pockets, by a relative rotational-translational motion betweensaid core (20) and said pocket member (11); the method beingcharacterized in that it further comprises: a step of axiallytranslating (105) the secondary structure (11B) with respect to mainstructure (11A), for inserting, into said further pocket (11B′) of thesecondary structure (11B), a further end portion (2A) of said array (T1)of end portions; and a second step of simultaneous twisting (106), bymeans of a further relative rotational-translational motion between saidcore (20) and said pocket member (11), the arc of end portions, which isinserted into the arc of pockets (R1) of the main structure (11A), andthe further end portion (2A, 2A′), which is inserted into the furtherpocket (11B) of the secondary structure (11B).
 2. Twisting method (100)according to claim 1, comprising a step, before the first twisting step(104), of making the secondary structure (11B) to take up an axiallybackward operating position with respect to main structure (11A), suchas, while said arc of end portions is inserted in the arc (R1) ofpockets, the further end portion (2A) may be positioned outside thefurther pocket (11B) at a certain axial distance from the insertionopening (11B″) of such pocket (11B).
 3. Twisting method according toclaim 2, wherein, during the first twisting step (104), said further endportion (2A) remains outside the further pocket (11B).
 4. Twistingmethod (100) according to claim 3, wherein, before the first twistingstep (104), while said arc of end portions is inserted into the arc (R1)of pockets, the further end portion is axially offset with respect tothe further pocket (11B) by a predetermined angle with respect totwisting axis (Z-Z), and wherein, at the end of first twisting step(104), the further end portion is axially aligned with the furtherpocket (11B).
 5. Twisting method (100) according to claim 1, wherein thestep of axially translating (105) comprises a step of arranging theinsertion opening (11B″) of the further pocket (11B) flush orsubstantially flush with the insertion openings (11A″) of the pockets ofsaid arc (R1).
 6. Twisting fixture (10) for twisting free end portions(2A, 3A, 2A′, 3A′) of bar conductors (1, 1′) for a stator or rotorwinding of an electrical machine, comprising at least one pocket member(11) extended about a twisting axis (Z-Z), said pocket member beingprovided with a circular array (S1) of pockets having its center on thetwisting axis (Z-Z), each pocket (11A′, 11B) being provided with aninsertion opening (11A″, 11B″), which is adapted to be passed through byone of said free end portions (2A, 2A′) for inserting such portion intosaid pocket, the pocket member (11) including: a main structure (11A)adapted to define an arc (R1) of adjacent pockets of said array (S1); asecondary structure (11B), which is movably mounted with respect to themain structure (11A) and is provided with a further pocket (11B′) ofsaid array (S1); the twisting fixture (10) being characterized in thatthe secondary structure (11B) is axially slidably mounted (Z-Z) withrespect to the main structure (11A).
 7. Twisting fixture (10) accordingto claim 6, wherein the secondary structure (11B) is slidable withrespect to main structure (11A) only in the direction of the twistingaxis (Z-Z).
 8. Twisting fixture (10) according to claim 6, wherein thesecondary structure (11B) is such as to take up: an axially backwardoperating position, wherein the secondary structure (11B) defines arecess (13) of the pocket member (11), and wherein the insertion opening(11B″) of the further pocket (11B′) is positioned at a first axialdistance (Z-Z) from the insertion openings (11A″) of the pockets (11A)of said arc (R1); and an axially forward operating position, withrespect to said backward position, wherein the insertion opening (11B″)of said further pocket (11B′) is positioned at a second axial distancefrom the insertion openings (11A″) of the pockets (11A) of said arc(R1).
 9. Twisting fixture (10) according to claim 8, wherein in saidforward position, the insertion opening (11B″) of the further pocket(11B′) is flush or substantially flush with insertion openings (11A″) ofthe pockets (11A) of said arc (R1).
 10. Twisting fixture (10) accordingto claim 6, wherein the further pocket (11B′) is positioned adjacent toa pocket (11A) of said arc (R1) and wherein the pockets (11A) of saidarc (R1) are angularly and uniformly spaced to each other by apredetermined angle (A1) with respect to the twisting axis (Z-Z), thefurther pocket (11B′) being angularly spaced from said adjacent pocket(11A) by an angle which is different from said predetermined angle. 11.Twisting fixture (10) according to claim 6, wherein the secondarystructure (11B) is provided with a plurality of said further pockets(11B″).
 12. Twisting fixture (10) according to claim 6, wherein thesecondary structure (11B) is coupled to the main structure (11A) bymeans of a precision coupling for allowing said axial sliding (Z-Z) ofsecondary structure (11B).
 13. Twisting fixture (10) according to claim12, wherein, in order to provide said precision coupling, the pocketmember (11) includes a slide seat (12), in which the secondary structure(11B) may slide, the slide seat (12) being defined by twocircumferentially opposed guiding walls (12′, 12″) of main structure(11A).
 14. Twisting fixture (10) according to claim 6, wherein thepocket member (11) comprises of a plurality of said secondary structures(11B).
 15. Twisting apparatus (200) comprising a twisting fixture (10)as defined in anyone of claims 6 to 14.